This application relates to opto-electronic devices and techniques for generating optical pulses, and more particularly, to optical pulse generation and synthesis based on Brillouin selective sideband amplification.
Optical waves can be used as carriers and modulated by using optical modulators to carry radio frequency (RF) signals. This combination of RF technology and photonic technology can be used to achieve certain advantages and provide new opto-electronic devices and applications in signal processing and communications.
One class of such opto-electronic devices use optical fibers or other optical media to optically amplify a RF signal superimposed on an optical carrier via Brillouin selective sideband amplification. This is described in U.S. Pat. 5,917,179 to Yao. This process uses a nonlinear optical process in which an optical pump beam can be injected into a Brillouin optical medium to produce an acoustic grating moving in the direction of the pump beam based on the electrorestrictive effect. This grating interacts with the pump beam to produce a backscattered Brillouin optical wave at a frequency less than that of the pump beam. When a narrowband seed signal, which is in the opposite direction of the pump wave and at the same frequency of the Brillouin optical wave, is injected into the medium, the interaction between the seed signal and the pump wave can significantly enhance the acoustic grating and convert the spontaneous Brillouin scattering into a stimulated Brillouin scattering (SBS). The stimulated back scattering light adds up in phase with the seed signal to produce an amplified seed signal. This Brillouin amplification can be used to implement a signal amplification scheme to selectively amplify a RF sideband in a modulated optical signal.
One application of this Brillouin selective sideband amplification is to selectively amplify multiple desired RF sidebands to generate optical pulses based on the interference of the amplified RF sidebands in the time domain. U.S. patent application Ser. No. 09/006,845 filed on Jan. 14, 1998 by Yao discloses a system where multiple pump beams from multiple pump lasers are used to amplify selected RF sidebands that are in phase with one another to generate optical pulses.
The systems and techniques of the present disclosure include a system that uses a common RF signal to modulate both a signal beam to produce multiple RF sideband signals and a single pump beam to produce multiple pump beams. RF sideband signals and multiple pump beams are sent into a Brillouin medium in opposite directions. The frequencies of the signal beam and the single pump beam are selected relative to each other so that the Brillouin signals generated by the pump beams overlap with the RF sideband signals to effectuate Brillouin selective sideband amplification of RF sideband signals.
The frequency of the single pump beam may be actively controlled to maintain the proper frequency overlap between the RF sideband signals and the respective Brillouin signals by adjusting a single pump laser that produces the single pump beam. In addition, the system may place the Brillouin medium between a polarizing beam splitter and a Faraday reflector to reduce the system sensitivity to the polarization states of the signal beam and the single pump beam and to double the Brillouin gain by passing the RF sideband signals and the pump beams through the Brillouin medium twice.